1. Field of the Invention
This invention relates to an electrode implantation device for placement of a microstimulator or microsensor in living tissue.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Microstimulators are small, implantable electrical devices that pass a signal to living tissue in order to elicit a response from a nerve or muscle. Microsensors are similar electrical devices except that they detect electrical and other signals that are generated by living tissue. The term microstimulator applies equally to both microstimulators and microsensors. The use of microstimulators or microsensors which are implanted in living tissue to stimulate a muscle function by either stimulating a nerve or the muscle itself are well known. The microstimulators receive power and control signals by inductive coupling of magnetic fields generated by an extracorporeal antenna rather than requiring any electrical leads. See for example, U.S. Pat. Nos. 5,193,539; 5,193,540; 5,324,316; 5,405,367; 6,175,764; 6,181,965; 6,185,452; 6,185,455; 6,208,894; 6,214,032; and 6,315,721, each of which is incorporated in its entirety by reference herein. These microstimulators are particularly advantageous because they can be manufactured inexpensively and can be implanted by minimally invasive surgery by injection. Additionally, each implanted microstimulator can be commanded, at will, to produce a well-localized electrical current pulse of a prescribed magnitude, duration and/or repetition rate sufficient to cause a smoothly graded contraction of the muscle in which the microstimulator is implanted.
While primarily designed to reanimate muscles so that they can carry out purposeful movements such as locomotion, the low cost, simplicity, safety and ease of implantation of these microstimulators suggests that they may additionally be used to conduct a broader range of therapies in which increased muscle strength, increased muscle fatigue resistance and/or increased muscle physical bulk are desirable; such as therapies directed to muscle disorders. For example, electrical stimulation of an immobilized muscle in a casted limb may be used to elicit isometric muscle contractions that prevent atrophy of the muscle for the duration of the casting period and facilitate rehabilitation after the cast is removed. Similarly, repeated activation of microstimulators injected into the shoulder muscles of patients suffering from stroke enable the paretic muscles to retain or develop bulk and tone, thus helping to offset the tendency for such patients to develop subluxation at the shoulder joint. Use of microstimulators to condition perineal muscles increases the bulk and strength of the musculature in order to maximize its ability to prevent urinary or fecal incontinence. See for example, U.S. Pat. No. 6,061,596, which is incorporated in its entirety by reference herein.
Microstimulators, as exemplified by the BION® of Advanced Bionics Corporation, are typically elongated devices with metallic electrodes at each end that deliver electrical current to the immediately surrounding living tissues. The microelectronic circuitry and inductive coils that control the electrical current applied to the electrodes are protected from the body fluids by a hermetically sealed capsule. This capsule is typically made of a rigid dielectric material, such as glass or ceramic, which transmits magnetic fields but is impermeable to water.
Often, while placing the miniature microstimulator in living tissue, the orientation of the microstimulator changes slightly such that the microstimulator is not in fact in electrical contact with the nerve, requiring reorientation of the microstimulator. The microstimulator may move from the desired location at any point in the surgical implantation procedure. If the microstimulator moves, it may be at a significant distance from the nerve that is to be stimulated or sensed. Consequently, more energy is needed from the microstimulator to stimulate the nerve, unless the microstimulator is repositioned closer to the nerve. While such microstimulators may be injected, the actual placement requires first locating the desired end point near the nerve or muscle. The known method of placement involves locating the nerve with an electric probe, placing a hollow implantation tool over the electric probe and removing the electric probe to allow the miniature microstimulator to be passed down the length of the hollow implantation tool. The implantation tool is then removed, leaving the microstimulator implanted at or near the desired location. If there is a problem with the function or location of the microstimulator, then additional surgery must be performed to remove or relocate the microstimulator, imposing risk, discomfort and potential tissue damage to the patient.
Using a known implantation tool, as disclosed in U.S. Pat. No. 6,214,032, to implant a microstimulator, may lead to the device being located remotely from the desired nerve. In this approach, an electrically stimulating trocar is first used to locate the desired nerve. The trocar is removed, after a cannula is slid along the trocar to be next to the nerve. Then the microstimulator is placed next to the nerve by inserting the microstimulator into the cannula and pushing the microstimulator to the end of the cannula, where it is ejected and is left behind, after the cannula is removed. The problem is that once the electrically stimulating trocar is removed, there is no way to detect movement of the cannula. Thus, the microstimulator may be left some distance from the desired location, as was determined by the stimulating trocar. This displacement from the optimum stimulating site unacceptably increases the power requirements and diminishes the battery life of the microstimulator.
Know devices such as that disclosed by Skakoon, US Pat. Publication US 2004/0044348, published Mar. 4, 2004, appear at first glance to provide a similar function. However, the device taught by Skakoon provides a means of retaining a medical electrical lead for passing through living tissue. It provides no method for removing the lead for implantation in living tissue. Further, it does not benefit from and provides no indication of depth of insertion into the living tissue since it passes completely thorough the tissue and does not teach implantation of the electrode in living tissue. The device taught by Skakoon teaches no means for retention of a flexible electrode during insertion since the device provides a single, collinear longitudinal slot with two fingers that cannot retain a flexible electrode lead in the device. Skakoon teaches that a portion of a catheter or a shunt or a medical electrical lead electrically conducting wire passes through the living tissue and that electrode terminates outside of the living tissue body, where it can be attached to another device. After passing through the tissue and not while within the tissue, the electrode is removed from the insertion device by moving the lead in a direction that is perpendicular to the longitudinal axis of the device.
Therefore, it is desired to have a method of implantation of a flexible electrode that ensures that the microstimulator is properly located and is implanted in an optimum position prior to removing the electrode implantation tool that is utilized during surgery to place the electrode lead.